Field of Invention
This invention pertains generally to mixers for aseptic liquids and, more particularly, to a magnetically coupled mixer with means for controlling friction between thrust bearings in the mixer.
Related Art
Magnetically coupled mixers are widely used for mixing liquids in sealed vessels. Such mixers typically have means for generating a rotating magnetic field outside the vessel and an impeller within the vessel which is coupled to the rotating field by magnets affixed to the impeller. With magnetic coupling, no drive shaft penetrates the vessel, and the problems associated with sealing around rotating shafts are avoided.
Magnetically coupled mixers heretofore provided do, however, have certain limitations and disadvantages. The impeller is commonly mounted on bearings which include thrust surfaces that rub together, producing friction, wear, and particles that can contaminate an otherwise sanitary environment within the vessel. While there have been some attempts to avoid such problems by levitating the impeller to separate the thrust bearing surfaces and keep them from contacting each other when the mixer is operating, that is not an entirely satisfactory solution because it gives rise to other problems, such as wobbling of the impeller.